This invention relates to a digital transmission system employing a transmitter and a receiver and more particularly to such a system employed or incorporated with a security system, such as a fire and burglar alarm apparatus.
The prior art is replete with a number of systems which are referred to as wireless systems. Essentially, such sustems are used as automatic garage door openers, remote control and so on. These systems transmit a unique code which consists of a predetermined number of bits arranged to provide a unique address to therefore enable the receiver to discriminate against various signals in order to only respond to the correct signal. In the case of a garage door for example, one would desire only to open the correct door and not other doors which may employ similar components.
Such wireless systems have been employed in the security field and serve to transmit a unique address when premises which are monitored indicate an intrusion. The advantage of such wireless systems is apparent as they eliminate the necessity for hard wired connections to a monitoring location. The elimination of such hard wiring is particularly advantageous in regard to urban residences and commercial establishments.
In regard to a security system, the apparatus which transmits a digital signal via a transmitter has to be reliable in order to permit accurate determination of an intrusion condition, thereby enabling a proper response. Preferably, the system should be economical to manufacture and relatively simple in operation so that it can be easily maintained and provided for.
Based on the nature of such systems, it is further desirable to monitor the status of an intrusion loop which may include both fire and burglar detectors to determine whether or not the loop is secure and hence, whether or not a true intrusion is present. Upon detection of such an intrusion, the system will transmit a unique code indicative of the premises which are monitored to enable a receiver to respond to the alarm condition and hence, to notify the proper authorities of the intrusion. Transmitting apparatus should be self-contained so that it may be employed at any desired location, such as a window, a door, or some other area which is to be monitored. Preferably, the system should be battery operated and provide an indication of the battery strength to enable replacement of batteries when the voltage falls below a predetermined level.
As indicated, many systems exist in the prior art which employ digital wireless control signals comprising different modulation techniques in an attempt to implement a reliable and accurate apparatus. Many of these techniques incorporate a form of pulse width modulation wherein the width of a pulse is varied according to whether or not the signal to be transmitted is a 0 or a 1. Other systems employ frequency shift modulation to enable a suitable response. As indicated, the majority of such systems are employed as in garage door activation schemes, remote radio control, and other types of control apparatus.
It is an object of the present invention to provide a digital wireless transmission system which is adapted to operate with an intrusion system to enable the transmission and reception of a suitable code signal when a monitored premises is intruded upon. The system to be described is simple to operate and economical to manufacture, while providing a continuous monitoring of the status of the premises and suitable indications of the battery condition at the transmitter.